The present invention relates to a three-dimensional graphic display apparatus for performing a hidden surface removal and color blending, and particularly to a configuration of a special purpose memory for graphics and a configuration of a graphic display apparatus using the special purpose memory for graphics.
A conventional memory for graphics comprises a normal dynamic RAM and a serial buffer as disclosed in Japanese Laid-Open Patent Application No. 59-131979 and U.S. patent application Ser. No. 427,236, now U.S. Pat. No. 4,562,435. According to the disclosure, a first port capable of providing a random access and a second port capable of reading display data are of substantially independently accessible memories, which were able to make a great increase in performance of both the random access and the reading of the display data as compared with the normal dynamic RAM.
As shown in FIG. 3, a three-dimensional graphic display apparatus using the conventional memory for graphics comprises: a drawing processor 300 including a pixel generator 301 for developing information about a straight line and a triangle supplied from a CPU 200 into pixel information, a memory controller 302 for converting XY coordinates of the developed pixel to an address in a special purpose memory 600, comparing the result of blending of an intensity of the developed pixel with intensities of pixels stored in the special purpose memory 600 and a Z coordinate, performing a hidden-surface removal for displaying preceding pixels for every pixel based on a result of comparing a Z coordinate, performing a WIND (Window Identify) comparison for controlling writing, and performing memory control for controlling reading of the information from the special purpose memory 600 when the information is determined and writing of the information into the special purpose memory 600 in accordance with the determined address, intensity, Z coordinate and the absence or presence of writing, and a serial buffer controller 303 for generating a signal for controlling display data sent to a RAMDAC, so as to be supplied to a serial buffer 602 of the special purpose memory 600; and the special purpose memory 600 including a memory cell 601 for holding pixel information comprised of intensity information, Z coordinate information and window information therein and the serial buffer 602 holding pixel data for display therein.
When it is desired to improve the performance of writing the pixel data into the special purpose memory, the prior art has increased the number of data signal lines or conductors between the drawing processor and the special purpose memory. However, when one attempts to realize the drawing processor and the special purpose memory in the form of an LSI, a problem arises that limitations are imposed on the number of the signal conductors.
Further, a problem arises when the screen is smoothly switched from one screen to another by separating a rewrite special purpose memory and a display special purpose memory from each other in a state in which a plurality of images to be displayed are being stored in the memory cell of the special purpose memory. When it is desired to realize a double buffer function for selecting one image for each pixel, it is necessary to output or generate a serial buffer's output corresponding to a plurality of pixels from the special purpose memory and the number of signal conductors used for the special purpose memory increases.